Method for removing suspended solids from aqueous fluids

ABSTRACT

A method for cleaning solids-laden aqueous fluids uses an apparatus comprising a settling tank having a sloping floor, which drops off into a collection area; primary and secondary mixing tanks, the lower regions of which are in fluid communication via fluid transfer means; and agitators in each of the mixing tanks. Solids-laden fluid is introduced into the primary mixing tank along with selected coagulant and/or flocculent chemicals, whereupon the agitator in the primary mixing tank is actuated to induce downward fluid flow toward the fluid transfer means and into the secondary mixing tank. The agitator in the secondary mixing tank is actuated to induce upward fluid flow in the secondary mixing tank, from which the fluid mixture overflows into the setting tank. Solids settle or precipitate into the settling tank, and then move downward along the settling tank&#39;s sloped floor and into the collection area, from which the solids can be removed for further treatment or disposal. Clean water is collected from the upper region of the settling tank, preferably via a spillway along the perimeter of the settling tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 11/928,107, filedon Oct. 30, 2007, now U.S. Pat. No. 7,771,594, which claims the benefitof Provisional Application No. 60/911,984, filed on Apr. 16, 2007. Bothsaid applications are incorporated herein by reference in their entiretyfor continuity of disclosure.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for removingsuspended solids from aqueous fluids, and from water-based drillingfluids in particular.

BACKGROUND OF THE INVENTION

It is often necessary or desirable, in various industrial applications,to treat solids-laden aqueous fluids to remove the solids and recoversubstantially clean water for re-use. A particular example is found indrilling operations in the petroleum industry, where water andwater-based fluids are commonly used as drilling fluids (or drilling“muds”), for purposes including cooling of the drill bit and removingdrill cuttings from the well bore. The drilling fluid is injected downthe drill stem and exits through the drill bit, and then is forced tothe ground surface through the annular space between the drill stem andthe well bore, carrying excavated material (i.e., cuttings) to thesurface in suspension. The “used” fluid is then processed to remove thesuspended solids, which are then disposed of, leaving substantiallyclean water than can be re-used in the well, or used for other purposes.

There are various known methods and apparatus for removing solids fromaqueous fluids, involving the use of some combination of settling tanks,mechanical agitation, chemical treatment (e.g., usingprecipitation-enhancing agents such as coagulants and flocculants),and/or mechanized transport of settled or precipitated solids. Thepresent invention teaches an improved apparatus and method for removingsuspended solids from aqueous fluids, using lower amounts of coagulantsand flocculants than known systems, and without requiring conveyors orother mechanized means for transporting settled or precipitated solidsfrom the apparatus.

BRIEF DESCRIPTION OF THE INVENTION

Conventional wisdom in the field of the invention has been thatflocculants cannot be effectively used in conjunction with agitation(the thinking being that agitation causes flocculants to loseeffectiveness). However, the inventors have discovered that thisconventional view is not necessary correct, as the present inventionprovides a way of using flocculants with agitation in an effectivemanner, in conjunction with regulation of agitator operation to suitvarious operational factors.

In accordance with the invention, a flow of solids-laden aqueous fluidis introduced into a primary mixing tank which is in fluid communicationwith a secondary mixing tank by means of fluid transfer means (such as atank opening or conduit) connecting the lower regions of the primary andsecondary mixing tanks. Selected coagulant and/or flocculent chemicalsare introduced into the primary mixing tank and mixed with thesolids-laden aqueous fluid by using agitator means preferably configuredto urge or direct the mixture downward within the primary mixing tank,and toward and through the fluid transfer means into the secondarymixing tank. The secondary mixing tank in turn has agitator meanspreferably configured to urge or direct the mixture upward within thesecondary mixing tank. The secondary mixing tank is provided withoverflow means (such as a scupper or conduit) whereby the mixture of thesolids-laden aqueous fluid and chemical additives flows out of an upperregion or zone of the secondary mixing tank into a larger settling tank,which is preferably but not necessarily directly adjacent to the primaryand secondary mixing tanks.

The settling tank has a sloping floor which drops off into a collectionarea at the settling tank's “deep end”, such that solids and sludge thatsettle or precipitate from fluid in the settling tank will tend to movedown the sloping floor toward the collection area. One or more sludgeoutlet ports are provided in association with the collection area, tofacilitate removal of accumulated sludge and solids from the collectionarea (preferably using suitable pumps) to external treatment equipment(such as centrifuges) or to disposal facilities.

The secondary mixing tank is preferably located close to the deep end ofthe settling tank so that solids settling or precipitating out of thechemically-treated mixture entering the settling tank from the secondarymissing tank's overflow means will have a shorter travel distance to thecollection area.

As solid materials settle out of the aqueous liquid mixture in thesettling tank, a zone of comparatively clean water forms in the upperregion of the settling tank. This clean water can be drawn or decantedfrom the upper region of the setting tank by any suitable means. Inpreferred embodiments, however, the settling tank is provided with aspillway running along a portion of the upper perimeter of the settlingtank, with one or more gates operable to permit flow of clean water fromthe settling tank into the spillway, from which the clean water can becollected for storage or direct re-use as desired. The spillway andgates can also be used for introducing clean water into the settlingtank to regulate the concentration of solids in the liquid mixture inthe settling tank.

By providing two interconnected mixing tanks, with agitation meansadapted to induce or promote swirling fluid flow downward within theprimary mixing tank and upward within the secondary mixing tank, theapparatus helps to keep additive chemicals (e.g., coagulants and/orflocculants) thoroughly mixed with the solids-laden fluid prior to beingdischarged into the settling tank. This enhances the effectiveness ofthe chemicals and thus results in lower chemical consumption compared toother methods for removing solids from aqueous fluids.

Accordingly, in a first aspect the present invention is a water recoveryapparatus for recovering water from aqueous fluids containing suspendedsolid matter, comprising:

-   -   (a) a settling tank having a sloping floor extending from an        upper end to a lower end;    -   (b) a collection chamber adjacent to, and having a floor lower        than, said lower end of the settling tank's sloping floor, said        collection chamber having an outlet port;    -   (c) a primary mixing tank;    -   (d) primary agitation means associated with the primary mixing        tank;    -   (e) a secondary mixing tank;    -   (f) secondary agitation means associated with the secondary        mixing tank;    -   (g) fluid transfer means whereby fluids can flow from a lower        region of the primary mixing tank into a lower region of the        secondary mixing tank; and    -   (h) overflow means whereby fluids can flow from an upper region        of the secondary mixing tank into the settling tank.

In a second aspect, the present invention is a water recovery method forrecovering water from aqueous fluids containing suspended solid matter,comprising the steps of:

-   -   (a) providing a water recovery apparatus as described above in        connection with the first aspect of the invention;    -   (b) introducing a flow of solids-laden aqueous fluid into the        primary mixing tank of the water recovery apparatus;    -   (c) introducing selected amounts of chemical precipitation        enhancement agents into the primary mixing tank, said chemical        agents being selected from the group consisting of coagulants        and flocculants; and    -   (d) activating the primary and secondary agitation means of the        water recovery apparatus so as to:        -   d.1 mix the precipitation enhancement agents with the            solids-laden aqueous fluid, creating a fluid mixture;        -   d.2 induce flow of the fluid mixture from the primary mixing            tank into a lower region of the secondary mixing tank via            the fluid transfer means; and        -   d.3 induce flow of the fluid mixture upward from the            secondary mixing tank into the settling tank via the            overflow means;    -   (e) allowing solids to precipitate out of the fluid within the        settling tank and to accumulate in the collection area of the        settling tank, with any solids contacting the sloped floor of        the settling tank floor being urged toward the collection area        by gravity;    -   (f) collecting clarified fluid from the spillway; and    -   (g) discharging solids-laden fluid from the collection area for        dewatering in a centrifuge.

Preferably, the primary agitation means is adapted to induce a downwardfluid current within the primary mixing tank, and the secondaryagitation means is adapted to induce an upward fluid current within thesecondary mixing tank. For example, the primary and secondary agitationmeans can each be provided in the form of conventional mixers oragitators having motor-driven vertical shafts that rotate propeller-typeagitator elements, with the pitch of the agitator blades or paddlesbeing configured to suit the desired fluid current (i.e., the pitch ofthe agitator blades for the primary agitation means would be opposite tothat of the secondary agitation means). Alternatively, the respectiveupward and downward currents in the primary and secondary mixing tankscould be initiated by using agitator motors turning in oppositedirections.

In preferred embodiments, the apparatus also comprises one or morechemical mixing tanks, plus means for conveying fluids from the chemicalmixing tank to the primary mixing tank.

Also in preferred embodiments, the apparatus further comprises agenerally horizontal spillway adjacent to an upper region of thesettling tank. The spillway has a clean water outlet port plus one ormore gates operable to allow fluid flow from the settling tank into thespillway or from the spillway into the settling tank. The spillway mayalso include outlet means whereby fluids may be collected from thespillway. The spillway may further have a gate operable to allow fluidflow from the spillway into the primary mixing tank, plus a gateoperable to allow fluid flow from the spillway into the secondary mixingtank. In embodiments incorporating a chemical mixing tank and aspillway, the spillway preferably has a gate to allow fluid flow fromthe spillway into the chemical mixing tank.

In particularly preferred embodiments, the apparatus also incorporates aplurality of spaced and substantially vertical baffles extending acrossthe settling tank transverse to the slope of sloped floor of thesettling tank. Each baffle has an upper edge and a lower edge, and thelower edge is disposed a selected distance above the sloped floor. Eachbaffle is provided with a baffle adjacent to the baffle's upper edge,plus gate actuation means for operating the baffle gate between a closedposition and an open position. Preferably, the lateral positions of thebaffle gates are staggered from one baffle to the next, so as to inducea meandering or serpentine pattern of liquid flow in the settling tank.

In embodiments having transverse baffles, the apparatus preferablyfurther includes baffle-cleaning means for removing solid matter builtup on the baffles. The baffle-cleaning means may include a wash piperunning adjacent to each baffle, with each wash pipe having a pluralityof orifices oriented to direct a stream of water from wash pipe toward aselected vertical face of the baffle.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying figures, in which numerical references denote like parts,and in which:

FIGS. 1A and 1B are isometric views of an apparatus for removingsuspended solids from aqueous solutions, in accordance with a firstembodiment of the present invention.

FIG. 2 is plan view of the apparatus of FIG. 1.

FIG. 3 is an elevation of a first side of the apparatus of FIG. 1.

FIG. 4 is an elevation of a second side of the apparatus of FIG. 1.

FIGS. 5A and 5B are isometric views of an alternative embodiment of theapparatus of the invention.

FIG. 6 is a transverse cross-section through the alternative embodimentof FIGS. 5A and 5B.

DETAILED DESCRIPTION OF THE INVENTION

As illustrated in FIGS. 1A and 1B, the apparatus 10 includes a settlingtank 20 having a first end 22 and a second end 24. Settling tank 20preferably (but not necessarily) has a generally rectangularconfiguration as shown, and is bounded by side walls 26A and 26B and endwalls 22A and 24A. Settling tank 20 has a sloped floor 28 which slopesdownward from an upper end 28U associated with first end 22 of settlingtank 20 to a lower end 28L close to but separated from second end 24 ofsettling tank 20. As may be required for structural purposes, suitablesupport posts or sub-walls (schematically indicated by reference numeral29 in FIGS. 3 and 4) may be provided to support sloping floor 28.

An open-top collection chamber 30 is formed between lower end 28L ofsloped floor 28 and end wall 24A, such that solid materials travelingdown sloped floor 28 can drop into collection chamber 30 upon reachinglower end 28L of sloped floor 28. Collection chamber 30 has a floor 32at an elevation lower than lower end 28L of sloped floor 28; collectionchamber floor 32 extends between end wall 24A and an intermediate wall34 which extends downward from lower end 28L of sloped floor 28 tocollection chamber floor 32.

Sloped floor 28 of settling tank 20 may be oriented at an angle between5 and 30 degrees to horizontal. However, it has been found that optimalperformance of apparatus 10 may be achieved with sloped floor 28 atapproximately 10 degrees to horizontal.

As shown in FIGS. 1A and 1B, apparatus 10 may be mounted on a suitableskid (generally indicated by reference numeral 15) to facilitate on-sitepositioning of apparatus 10 and to facilitate transportation ofapparatus 10 between worksites. However, this is not essential to theinvention.

Apparatus 10 also includes a primary mixing tank 40 and a secondarymixing tank 50. Also provided (as conceptually indicated in FIGS. 2, 3,and 4) are primary agitation means 42 for purposes of mixing oragitating fluids within primary mixing tank 40, and secondary agitationmeans 52 for purposes of mixing or agitating fluids within secondarymixing tank 50. There is no particular limitation on the type ofequipment that could be used for purposes of agitation means 42 and 52,but in the preferred embodiment of apparatus 10, agitators of a typewell known in the field (e.g., with a top-mounted motor rotating avertical shaft having paddles or blades mounted thereto) are used forthese purposes. The pitch of the agitator paddles or blades for primaryagitation means 42 will preferably be opposite to the blade/paddle pitchfor secondary agitation means 52, such that actuation of primaryagitation means 42 will tend to induce a downward fluid current withinthe primary mixing tank 40, and actuation of secondary agitation means52 will tend to induce an upward fluid current within secondary mixingtank 50. Alternatively, these desirable differential fluid currents mayinduced by using agitator motors turning in opposite directions.

In the illustrated embodiments, primary mixing tank 40 and secondarymixing tank 50 are in a side-by-side arrangement, separated by adividing wall 44. Primary mixing tank 40 and secondary mixing tank 50are in fluid communication through appropriate fluid transfer meanspermitting fluids to flow from a lower region of primary mixing tank 40into a lower region of secondary mixing tank 50. As shown in FIGS. 3 and4, this fluid transfer means may be provided in the form of a transferport 46 near the bottom of dividing wall 44. However, persons skilled inthe art of the invention will readily appreciate that the fluid transfermeans could take other forms (for example, a conduit extending betweenlower regions of primary mixing tank 40 and secondary mixing tank 50),without substantially affecting the operation of apparatus 10.

Apparatus 10 also includes overflow means in an upper region ofsecondary mixing tank 50, whereby fluids can overflow from secondarymixing tank 50 into settling tank 20, preferably but not necessarily inthe vicinity of second end 24 thereof (i.e., the deeper end). As shownin FIG. 2, the overflow means may be provided in the form of an overflowport 54 or scupper in a secondary mixing tank wall immediately adjacentto settling tank 20, such that fluids can flow from secondary mixingtank 50 through overflow port 54 directly into settling tank 20.However, the overflow means could be provided in other forms withoutdeparting from the scope of the present invention. For example, theoverflow means could be in the form of a conduit or spillway passingthrough or over a wall of secondary mixing tank 50. Furthermore, it isnot essential for any portion of secondary mixing tank 50 to beimmediately adjacent to settling tank 20, since the provision ofoverflow means in the form of a conduit or spillway would make itfeasible to have secondary mixing tank 50 separated from settling tank20.

Also in the illustrated embodiment, both primary mixing tank 40 andsecondary mixing tank 50 are disposed within the rectangular perimeterof the settling tank 20, with primary mixing tank 40 being adjacent toboth side wall 26B and end wall 24A, and with secondary mixing tank 50being adjacent to side wall 26B. However, this preferred arrangement isfor reasons of compactness and efficiency, and is not essential to theinvention; other functionally effective arrangements could be readilydevised without departing from the concept of the invention. Forexample, either or both of primary mixing tank 40 and secondary mixingtank 50 could be positioned outside settling tank 20, either adjacent toor spaced away from settling tank 20 (using an appropriate form ofoverflow means as previously discussed). Moreover, it is not essentialfor primary mixing tank 40 and secondary mixing tank 50 to be side byside; it would be functionally feasible for these components to beseparated from each other, in conjunction with an appropriate form offluid transfer means (such as a conduit).

In preferred embodiments of apparatus 10, and as shown in FIG. 1A, aclean-out port 41 is provided at the base of primary mixing tank 40 suchthat solids and sludge accumulating within primary mixing tank 40 can beconveniently washed into collection chamber 30 when settling tank 20 andcollection chamber 30 are empty. A similar clean-out port 51 is alsopreferably provided in association with secondary mixing tank 50.Clean-out ports 41 and 51 are provided with suitable gates which,although shown in their open positions in FIG. 1A, will be closed duringnormal operation of apparatus 10. As shown in FIGS. 2, 3, and 4, one ormore sludge outlet ports 36 are provided in association with collectionchamber 30, for conveying accumulated aqueous sludge from collectionchamber 30 to external treatment equipment or to disposal facilities. Inpreferred embodiments of the method of the invention, the sludge ispumped from collection chamber 30 to treatment equipment comprising oneor more centrifuges (not shown), and the clarified residual waterremaining after the centrifuges have removed the solids from the sludgecan be recycled for use in well-drilling operations, recycled for use inconjunction with apparatus 10 (as discussed below), or pumped to storagefor future use.

In the illustrated embodiment, two outlet ports 36 are shown extendingthrough end wall 24A; this is a preferred configuration, but otherfunctionally effective configurations are possible. In one preferredembodiment, each outlet port 36 comprises a 3-inch or 4-inch outlet pipefitted with a two-way manually-operated valve that can be connected to apump for conveying sludge to a centrifuge or disposal facility.

In preferred embodiments (and as illustrated in FIGS. 1A, 1B, 5A, and5B), apparatus 10 includes a generally horizontal, open-topped spillway60 adjacent to an upper region of settling tank 20. In the illustratedembodiments, spillway 60 runs longitudinally along side wall 26B, butthis particular arrangement is not essential to the invention; spillway60 could be provided in alternative configurations while retaining itsdesired function, as further described below. Spillway 60 has one ormore gates 62 that can be selectively opened to direct fluids fromsettling tank 20 into spillway 60, or to allow fluids to flow fromsettling tank 20 into spillway 60. In the preferred embodiment shown inthe Figures, in which primary mixing tank 40 and secondary mixing tank50 are disposed within the rectangular perimeter of settling tank 20adjacent to side wall 26B, spillway 60 has additional gates 62 that areselectively operable to direct fluids from spillway 60 into primarymixing tank 40 and/or secondary mixing tank 50 as may be desired.Spillway 60 preferably also has a clean water outlet port 61, tofacilitate diversion and collection of clean water from spillway 60 forother or future uses.

As described later in this specification, the preferred embodiment ofthe method of the present invention involves the step of introducingselected amounts of coagulants and/or flocculants into primary mixingtank 40, to be mixed with solids-laden aqueous fluid in primary mixingtank 40. For convenience in this regard, the preferred embodiment ofapparatus 10 incorporates one or more chemical mixing tanks 70,preferably including chemical agitator means 72. As shown in theFigures, chemical mixing tanks 70 may be conveniently located within theperimeter of settling tank 20, adjacent to end wall 22A. However, it isnot essential to the present invention for apparatus 10 to incorporatechemical mixing tanks, which could in fact be located away fromapparatus 10 (with suitable piping or other conduit means being providedfor conveying chemical solutions from chemical mixing tanks 70 toprimary mixing tank 40).

In embodiments of apparatus 10 that incorporate one or more chemicalmixing tanks 70, spillway 60 is preferably configured such that aportion of spillway 60 runs adjacent to chemical mixing tanks 70, withadditional gates 62 operable to allow fluids within spillway 60 to beselectively directed into chemical mixing tanks 70. In the illustratedembodiment, this preferred capability is provided by fashioning spillway60 in an L-shaped configuration, comprising a longitudinal leg 60Arunning adjacent to side wall 26B as previously described, and atransverse leg 60B running adjacent to the chemical mixing tanks 70.This allows clean water from spillway 60 to be used as make-up water forpurposes of preparing chemical solutions in chemical mixing tanks 70.(In this and similar contexts in this patent document, the term “cleanwater” refers to the comparatively clean water from upper regions ofsettling tank 20 after there has been significant or substantialsettlement or precipitation of solids from solids-laden fluid introducedinto settling tank 20).

The method of the present invention may be readily understood havingregard to the foregoing description of the apparatus 10 of theinvention. In general terms, the method of the invention can besummarized as a method for recovering water from aqueous fluidscontaining solid matter utilizing a selected embodiment of apparatus 10,and comprising the following steps:

-   -   introducing a flow of solids-laden aqueous fluid into primary        mixing tank 40;    -   introducing selected amounts of precipitation enhancement agents        such as coagulants and/or flocculants (preferably in aqueous        solution form) into primary mixing tank 40;    -   activating primary agitation means 42 and secondary agitation        means 52 (thus mixing the coagulants and/or flocculants into the        solids-laden fluid, and inducing or promoting flow of the fluid        mixture out of primary mixing tank 40 into secondary mixing tank        50 through transfer port 46, and out of secondary mixing tank 50        into settling tank 20 through overflow port 54);    -   allowing solids to settle and/or precipitate out of the fluid        mixture within settling tank 20 and to accumulate in collection        chamber 30 of settling tank 20 (with any solids contacting        sloped floor 28 of settling tank 20 being urged toward        collection chamber 30 with the assistance of gravity); and    -   conveying solids-laden sludge from collection chamber 30 through        outlet ports 36, to a disposal or treatment facility.

Persons skilled in the art will appreciate that some of the stepssummarized above may take place concurrently rather than sequentially,and that the specific order in which certain steps are initiated is notnecessarily essential to the method of the invention.

The method of the present invention is not dependent on the use of anyparticular type of coagulants or flocculants. The coagulants orflocculants to be used in a given application will be selected havingregard to case-specific parameters. In cases where the method is beingused to remove water from aqueous drilling fluids, these chemicalselection parameters may include the type and composition of thedrilling fluid, and the physical and chemical characteristics of thesubsurface formation materials being drilled through using the drillingfluid.

In preferred embodiments of the method, clean water is allowed tooverflow from settling tank 20 into spillway 60, and this clean watermay then be used in a variety of ways. For example, some of the cleanwater could be recycled into selected mixing tanks and/or chemical tanksas previously mentioned. Another possibility would be to use clean watercollected from spillway 60 (e.g., via clean water outlet port 61) in thepreparation of aqueous drilling muds for purposes of drillingoperations. Alternatively, the clean water can be conveyed to a storagetank for later use.

It should be noted that the provision of a spillway 60 is not essentialfor purposes of collecting clean water from settling tank 20. Inalternative embodiments of the apparatus and methods of the invention,clean water could also be collected by simply providing a scupper oroutflow pipe in an upper region of settling tank 20, preferably near the“deep end” 24 of settling tank 20. Persons of ordinary skill in the artwill appreciate that clean water collected by such alternative means canbe readily redirected to mixing tanks and/or chemical tanks usingsuitable pumps and piping arrangements.

In preferred embodiments of the method, sludge from collection chamber30 will be directed to one or more centrifuges, which will remove solidmatter to produce clarified residual water that may be as clean as oreven cleaner than the “clean water” remaining in the upper regions ofsettling tank 20 after settlement and/or precipitation of solids aspreviously described. The residual water from the centrifuges may berecycled to settling tank 20 and/or the mixing tanks and/or the chemicaltanks (either directly or via spillway 60), or it may be diverted foruse in preparing drilling fluids, or it may be collected in a storagetank for future use.

It is well known to mix coagulants and/or flocculants into asolids-laden aqueous fluid to promote settlement or precipitation ofsolids from the fluid. However, the use of twin mixing tanks as in thepresent invention (i.e., primary mixing tank 40 and secondary mixingtank 50, with a low-level transfer port connecting them), induces fluidflow downward within primary mixing tank 40 and then upward withinsecondary mixing tank 50. As a result, the chemicals remain morethoroughly dispersed within the fluid, and for a comparatively longertime than in known methods, due to the current induced in the fluidmixture as it flows from primary mixing tank 40 into secondary mixingtank 50 and then spills from secondary mixing tank 50 into settling tank20. This type of flow or current would not occur if only a single mixingtank were used, even in conjunction with an agitator. Due to the use ofthe twin mixing tank arrangement of the present invention, though, theimproved chemical dispersal increases the chemicals' efficiency, therebyreducing the required amount of chemicals as compared with knownsystems. The process efficiency gains thus provided in accordance thepresent invention result not only in reduced chemical costs, but alsoreduced equipment costs (since smaller chemical pumps and hoses can beused) and reduced energy costs (since the smaller chemical pumps willconsume less energy).

FIGS. 5A, 5B, and 6 illustrate a particularly preferred embodiment ofapparatus 10, in which settling tank 20 has one or more baffles 110 areprovided at selected intervals along the length of settling tank 20 andextending between side walls 26A and 26B, transverse to the slope offloor 28. Baffles 110 are oriented substantially vertically, with theirlower edges 112 disposed a selected distance above sloped floor 28 ofsettling tank 20, thus creating a lateral space 114 such that solidssettling or precipitating out of fluids introduced into settling tank 20can freely pass below baffles 110 en route to collection chamber 30. Theupper edges 116 of baffles 110 are disposed at a selected height,typically close to the fluid level in settling tank 20 during normaloperation of apparatus 10.

Each baffle 110 preferably has a baffle gate 120 adjacent to upper edge116 and disposed toward one side of settling tank 20. Baffle gate 120may be of any suitable type (e.g., a swing gate, butterfly gate, orsliding gate), and will have manually-operated or mechanically-operatedactuation means (conceptually indicated in the Figures as a handle 122)for selectively operating baffle gate 120 between a closed position andan open position. As best seen in FIGS. 5A and 5B, the positions ofbaffle gates 120 preferably alternate in staggered fashion (i.e., withthe gate 120 for one baffle 110 being adjacent one side of settling tank20, and with the gate 120 of the next baffle 110 being adjacent theother side of settling tank 20).

When staggered baffle gates 120 are in the open position, fluids in theupper zone of settling tank 20 will be induced to follow a meanderingpath as it moves toward first end 22 of settling tank 20. Accordingly,the retention time of the fluid is increased relative to what it wouldbe without baffle gates 120 being open, thus enhancing the efficiency ofsolids removal using the apparatus 10 and method of the presentinvention.

The upper-zone flow induced by opening baffle gates 120 (irrespective oftheir lateral locations in baffles 110) can have the additionalbeneficial effect of inducing a current which enhances thegravity-assisted flow of fluids and solids along sloped floor 28 towardcollection chamber 30.

Preferably, in embodiments incorporating baffles 110, apparatus 10 alsoincludes baffle-cleaning means for removing solid matter that may buildup on the vertical faces of baffles 110. As illustrated in FIGS. 5A, 5B,and 6, this may be accomplished by running a wash pipe 130 laterallyalongside each baffle 110, at a level above lower edge 112 of baffle110, with each wash pipe 130 having a plurality of nozzles or orifices132 and oriented so as to direct a stream of water from wash pipe 130toward the vertical face of baffle 110. As illustrated, wash water maybe fed to wash pipes 130 from a water manifold 134 running along oneside of settling tank 20, with the flow of water into wash pipes 130being selectively controlled by valves 136 at the junctures between washpipes 130 and manifold 134. Wash water may be provided from anyconvenient source, including spillway 60 or a source external toapparatus 10.

Effective results have been achieved in certain applications usingnominal 2-inch diameter wash pipes having orifice sizes varying from¼-inch to ⅜-inch diameter (as shown by way of example in FIG. 6).However, the size of wash pipes 130 and the size and spacing of orifices132 may be selected to suit specific process design requirements.

As shown in FIGS. 5A, 5B, and 6, apparatus 10 is preferably providedwith a catwalk 105 to facilitate access to the baffle gate actuationmeans and valves 136.

In FIGS. 5A, 5B, and 6, numerical references to some components ofapparatus 10 have been omitted in the interests of clarity, tofacilitate illustration of additional features as described above.Reference may be had to the other Figures with respect to components notspecifically referenced in FIGS. 5A, 5B, and 6.

It will be readily appreciated by those skilled in the art that variousmodifications of the present invention may be devised without departingfrom the essential concept of the invention, and all such modificationsare intended to come within the scope of the present invention and theclaims appended hereto. It is to be especially understood that theinvention is not intended to be limited to illustrated embodiments, andthat the substitution of a variant of a claimed element or feature,without any substantial resultant change in how the invention works,will not constitute a departure from the scope of the invention.

In this patent document, the word “comprising” is used in itsnon-limiting sense to mean that items following that word are included,but items not specifically mentioned are not excluded. A reference to anelement by the indefinite article “a” does not exclude the possibilitythat more than one of the element is present, unless the context clearlyrequires that there be one and only one such element.

1. A method for recovering water from aqueous fluids containingsuspended solid matter, said method comprising the steps of: (a)providing a settling tank; a primary mixing tank; a secondary mixingtank; and fluid transfer means whereby fluids can flow from a lowerregion of the primary mixing tank into a lower region of the secondarymixing tank; said secondary mixing tank having overflow means wherebyfluids can flow from an upper region of the secondary mixing tank intothe settling tank; (b) providing primary and secondary agitation meansin association with the primary and secondary mixing tanks,respectively; (c) providing a generally horizontal spillway adjacent toan upper region of the settling tank, said spillway having: c.1 a firstgate operable to allow fluid flow from the settling tank into thespillway or from the spillway into the settling tank; and c.2 a secondgate operable to allow fluid flow from the spillway into a selected oneof the primary and secondary mixing tanks; (d) introducing a flow ofsolids-laden aqueous fluid into the primary mixing tank; (e) introducingselected amounts of precipitation enhancement agents into the primarymixing tank, said precipitation enhancement agents being selected fromthe group consisting of coagulants and flocculants; (f) actuating theprimary agitation means to mix the precipitation enhancement agents withthe solids-laden aqueous fluid within the primary mixing tank, and toinduce flow of the fluid mixture downward within the primary mixing tankand thence into the secondary mixing tank via the fluid transfer means;(g) actuating the secondary agitation means to induce flow of the fluidmixture upward within the secondary mixing tank and thence into thesettling tank via the overflow means; (h) allowing solids to precipitateout of the fluid mixture in the settling tank; and (i) collecting cleanwater from an upper region of the settling tank; wherein the methodcomprises the further steps of operating the first gate to allow cleanwater to flow from the settling tank into the spillway, and operatingthe second gate to allow clean water to flow from the spillway into theselected mixing tank.
 2. The method of claim 1 wherein the settling tankhas a sloping floor and a collection chamber adjacent to and lower thanthe lower end of the sloping floor, said collection chamber having anoutlet port, and comprising the further step of allowing precipitatedsolids to flow by gravity into the collection chamber.
 3. The method ofclaim 2, further comprising the step of conveying solids-laden sludgefrom the collection chamber through the outlet port.
 4. The method ofclaim 3, further comprising the step of separating water from thesolids-laden sludge in a centrifuge.
 5. The method of claim 1 whereinthe spillway further comprises a clean water outlet port, and whereinthe step of collecting clean water includes the step of operating thefirst gate to allow clean water to flow from the settling tank into thespillway and into the clean water outlet port.
 6. The method of claim 1wherein the step of introducing precipitation enhancement agents intothe primary mixing tank comprises the steps of preparing a chemicalsolution of precipitation enhancement agents in a chemical mixing tankand conveying the chemical solution from the chemical mixing tank to theprimary mixing tank.
 7. A method for recovering water from aqueousfluids containing suspended solid matter, said method comprising thesteps of: (a) providing: a.1 a settling tank having a sloping floor anda collection chamber adjacent to and lower than the lower end of thesloping floor, said collection chamber having an outlet port; a.2 aprimary mixing tank; a.3 a secondary mixing tank having overflow meanswhereby fluids can flow from an upper region of the secondary mixingtank into the settling tank; and a.4 fluid transfer means whereby fluidscan flow from a lower region of the primary mixing tank into a lowerregion of the secondary mixing tank; (b) providing primary and secondaryagitation means in association with the primary and secondary mixingtanks, respectively; (c) introducing a flow of solids-laden aqueousfluid into the primary mixing tank; (d) introducing selected amounts ofprecipitation enhancement agents into the primary mixing tank, saidprecipitation enhancement agents being selected from the groupconsisting of coagulants and flocculants; (e) actuating the primaryagitation means to mix the precipitation enhancement agents with thesolids-laden aqueous fluid within the primary mixing tank, and to induceflow of the fluid mixture downward within the primary mixing tank andthence into the secondary mixing tank via the fluid transfer means; (f)actuating the secondary agitation means to induce flow of the fluidmixture upward within the secondary mixing tank and thence into thesettling tank via the overflow means; (g) allowing solids to precipitateout of the fluid mixture in the settling tank, and allowing precipitatedsolids to flow by gravity into the collection chamber; and (h)collecting clean water from an upper region of the settling tank;wherein the settling tank further comprises a plurality of spaced andsubstantially vertical baffles extending across the settling tanktransverse to the slope of sloped floor of the settling tank, eachbaffle having: (i) an upper edge and a lower edge, said lower edge beingdisposed a selected distance above the sloped floor; (j) a baffle gateadjacent said upper edge; and (k) gate actuation means for selectivelyoperating the baffle gate between a closed position and an openposition; and wherein the method comprises the further step of openingthe baffle gates to facilitate fluid flow in an upper zone of thesettling tank.
 8. The method of claim 7 wherein the baffle gates of atleast one pair of adjacent baffles are laterally staggered, so as toinduce a meandering flow pattern of fluid flow in the upper zone of thesettling tank.
 9. The method of claim 7, further comprising the steps ofproviding baffle-cleaning means for removing solid matter built up onthe baffles, periodically actuating the baffle-cleaning means to removesolid matter from the baffles, and allowing the removed solid matter toflow into the collection chamber.
 10. The method of claim 9 wherein thebaffle-cleaning means comprises a wash pipe running adjacent to eachbaffle, with each wash pipe having a plurality of orifices oriented todirect a stream of water from wash pipe toward a selected vertical faceof the corresponding baffle.
 11. The method of claim 7 wherein the stepof introducing precipitation enhancement agents into the primary mixingtank comprises the steps of preparing a chemical solution ofprecipitation enhancement agents in a chemical mixing tank and conveyingthe chemical solution from the chemical mixing tank to the primarymixing tank.
 12. A method for recovering water from aqueous fluidscontaining suspended solid matter, said method comprising the steps of:(a) providing: a.1 a settling tank having a sloping floor and acollection chamber adjacent to and lower than the lower end of thesloping floor, said collection chamber having an outlet port; a.2 aprimary mixing tank; a.3 a secondary mixing tank having overflow meanswhereby fluids can flow from an upper region of the secondary mixingtank into the settling tank; and a.4 fluid transfer means whereby fluidscan flow from a lower region of the primary mixing tank into a lowerregion of the secondary mixing tank; (b) providing primary and secondaryagitation means in association with the primary and secondary mixingtanks, respectively; (c) introducing a flow of solids-laden aqueousfluid into the primary mixing tank; (d) introducing selected amounts ofprecipitation enhancement agents into the primary mixing tank, saidprecipitation enhancement agents being selected from the groupconsisting of coagulants and flocculants; (e) actuating the primaryagitation means to mix the precipitation enhancement agents with thesolids-laden aqueous fluid within the primary mixing tank, and to induceflow of the fluid mixture downward within the primary mixing tank andthence into the secondary mixing tank via the fluid transfer means; (f)actuating the secondary agitation means to induce flow of the fluidmixture upward within the secondary mixing tank and thence into thesettling tank via the overflow means; (g) allowing solids to precipitateout of the fluid mixture in the settling tank, and allowing precipitatedsolids to flow by gravity into the collection chamber; and (h)collecting clean water from an upper region of the settling tank;wherein a generally horizontal spillway is provided adjacent to an upperregion of the settling tank, and wherein a chemical mixing tank islocated adjacent to the spillway, said spillway having: (i) a first gateoperable to allow fluid flow from the chemical mixing tank into thespillway; and (j) a second gate operable to allow fluid flow from thespillway into the primary mixing tank; and wherein the step ofintroducing precipitation enhancement agents into the primary mixingtank comprises the steps of preparing a chemical solution ofprecipitation enhancement agents in the chemical mixing tank andconveying the chemical solution from the chemical mixing tank to theprimary mixing tank, and wherein the step of conveying the chemicalsolution from the chemical mixing tank to the primary mixing tankincludes the steps of operating the first gate to allow the chemicalsolution to flow from the chemical mixing tank into the spillway, andoperating the second gate to allow the chemical solution to flow fromthe spillway into the primary mixing tank.